FBI spokeswoman Sandy Breault said that authorities strongly believe 10-year-old Lyric Cook-Morrissey and 8-year-old Elizabeth Collins have not been killed.

She refused to say what led authorities to that conclusion, but told reporters that investigators are expanding their search beyond Iowa.

The announcement came a day after authorities said they believe the girls were abducted.

The girls disappeared around noon July 13 shortly after they left their grandmother's house near Evansdale in northeast Iowa. Their bikes and a purse were found on a path near Meyers Lake, prompting investigators to drag it last weekend and to begin draining it earlier this week.

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Elizabeth Collins, left, and Lyric Cook went missing in Evansdale, Iowa on Friday.

On Friday, authorities said they were treating the case as an abduction after an FBI dive team used sophisticated sonar to determine the girls' remains were not in the lake.

Breault says investigators are interviewing "persons of interest" in the case, whom she declined to identify.

On Friday, Rick Abben, chief deputy with the Black Hawk County Sheriff's office, had said investigators still had no single person of interest in the case. Abben said investigators had recovered some evidence and sent it to the Iowa Division of Criminal Investigation for analysis. He declined to say what the evidence was or where it was found.

Abben also confirmed that investigators had asked a judge to compel Lyric's father, 36-year-old Daniel Morrissey, who faces drug charges but is free on bond, to submit to closer watch by parole officers pending his trial.

He said the request -- which was granted on Thursday -- did not imply that Morrissey, who has stopped cooperating with investigators, was a suspect in the case.

"That was done so that we have a little bit closer ... supervision of people," Abben said. "We are not looking at anyone. Everyone is being checked into."